Linear alkylbenzene sulfonate is the most commonly used anionic surfactant in cleaning compositions due to its excellent overall performance. For this reason, more than 3 million tons of LAS are consumed each year worldwide. LAS presents an outstanding cost/performance ratio, good stability over long periods of time and compatibility with a wide range of detergent components. Further, it shows a high degree of synergism in combination with some ingredients commonly used in cleaning formulations.
LAS is produced by sulfonation of Linear Alkylbenzene (LAB) and subsequent neutralization of the corresponding sulfonic acid (HLAS). Linear alkylbenzene is synthesized by the alkylation of benzene with linear olefins. Traditional processes for alkylation of aromatics compounds use Friedel-Craft type catalysts, for example, hydrofluoric acid, aluminum trichloride and the like. These processes are well known and used commercially, yielding a high conversion (>99% by weight) to LAB with selectivity to 2-phenyl-derivative relatively low, less than 30% by weight (P. R. Pujado, Handbook of Petroleum Refining Process, Robert A. Meyers (Editor), 1986, p. 1-23.)
Recent developments using various types of zeolytes, mordenites and other type of products as alkylation catalysts describe the production of LAB with a 2-phenyl-derivative content in the range of 30% to 80% by weight (J. L. Berna Tejero, A. Moreno Danvilla U.S. Pat. No. 5,157,158, 1992; and J. L. G. De Almeida, M. Dufaux, Y. Ben Taarit y C. Naccache, Journal od the American Oil Chemist's Society, Vo. 71, No7, 675-694, 1994.).
LAB mixtures with external isomers content (2+3 phenyl) higher than 50% by weight are reported to provide after sulfonation and neutralization, a LAS with improved surface activity properties. These LAS however, show an important drawback caused by their low solubility in cold water conditions and high viscosity. In fact, LAS mixtures comprising more than 50% by weight of external isomers (2+3 phenyl) tend to form highly insoluble gels with high viscosity that makes them difficult to handle and process.
Earlier patent applications have attempted to improve the solubilization of LAS using different additives. Patent application WO 0040551 discloses the use of a commercial hydrotrope selected from the group of an alkylbenzene, an olefin, a methyl or ethyl ester of a carboxylic acid, an alkyl alcohol, non sulfonatable hydrotrope precursors, and mixtures thereof; either before or after sulfonation.
U.S. Pat. No. 6,133,217 discloses methods and compositions for the solubilization of linear alkylbenzene sulfonates in detergent formulations by the addition of one or more ethylene oxide/propylene oxide block copolymers.
Nevertheless, for LAS with very high concentrations of 2-phenyl-derivatives, none of the known hydrotropes seems to be suitable enough to sufficiently solubilize them and to reduce their viscosity. Moreover, the addition of hydrotrope precursors or hydrotropes increase the cost of the final cleaning composition formulations
Accordingly, it would be desirable to find a hydrotrope with better performance to solubilize and reduce the viscosity of LAS with a high content of external isomers as well as improving the solubility and viscosity of those LAS with low content of external isomer. It would be preferably that such hydrotrope belongs to the family of alkylbenzenes and more preferably that it could be obtained in the facilities where linear alkylbenzenes are produced without significant capital investment.